1. Field of the Invention
The present invention relates to the field of ultrasonic equipment and can be used in different technological devices for the transmission of acoustic energy into an acoustic load, for example, in heat and mass transfer processes, plastic welding, metal treatment, etc.
2. Description of Prior Art
Acoustic energy is usually transmitted into an acoustic load (liquid, polymeric or hard material) using an ultrasonic waveguide-radiator connected to an electro-acoustic transducer (magnetostrictive or piezoelectric). The tasks of the waveguide-radiator are to increase the amplitude of the transducer vibrations A up to the level necessary in a given technology, to match the energy of a transducer to an acoustic load, to uniformly distribute radiated acoustic energy throughout the volume of the medium being treated, and/or to facilitate reliable fastening of cutting and other tools to the waveguide radiator. Matching the energy of the transducer to the acoustic load means the development of a waveguide-radiator design that provides transmission of maximum acoustic power from the transducer into the load.
It is known that specific acoustic power radiated by a waveguide into an acoustic load, for instance into a liquid, is equal to w=0.5 ρCω2A2 [Wt/sq.m]. Here ρ is the density of liquid, C is the speed of sound in liquid, ω is the frequency of ultrasonic vibrations, and A is the amplitude of ultrasonic vibrations. The total acoustic power radiated into liquid is equal to W=wS [Wt]. Here S is the area of the radiating surface of the waveguide-radiator. Thus, it is evident that an increase in the total radiated acoustic power at constant load and frequency can be achieved by increasing either of the following two factors: the amplitude of output vibrations of the waveguide-radiator or the area of the waveguide-radiator's radiating surface. The amplitude of output vibrations cannot be increased above a certain level that corresponds to the fatigue strength of the waveguide-radiator material. Increasing amplitude above this level causes the waveguide-radiator to break down. Furthermore, a considerable increase in the amplitude of vibrations is not always justified from the technological point of view. It is also possible to increase the exit diameter of a rod waveguide-radiator up to a certain level that is equal to about λ/4 (where λ is the wavelength of ultrasound waves in the material of a thin-rod waveguide-radiator). When the waveguide-radiator exit diameter is larger than this value, radiation via the waveguide-radiator's side surfaces begins to have a strong effect, and calculation of the waveguide's acoustic properties becomes difficult to predict. Nevertheless, increasing the waveguide-radiator exit diameter up to a value close to λ/4 gives an opportunity to increase the radiated power by several times.
The closest device in its essence to the present invention is a known ultrasonic rod waveguide-radiator that has a shape converging (tapering) to a load. The shape of such a waveguide-radiator is determined by the fact that its gain factor of the amplitude of ultrasonic vibrations in the direction of an acoustic load must be higher than unity. To increase the radiating surface, a converging waveguide radiator is provided at the radiating exit end with a section in the form of a thin disk or plate having a large diameter, usually close to the waveguide-radiator entrance diameter. The presence of a short transition section of arbitrary shape between the waveguide radiator and the plate at its radiating end is also possible. This section is designed to increase the area of the exit radiating surface and consequently the acoustic energy radiated into a load.
Such a waveguide-radiator with a plate or disk at the end has substantial disadvantages. First, at a small value of the ratio of the length and diameter of the specified section (usually less than 0.5), instead of the axial (longitudinal) mode of vibrations which must occur in the body of the waveguide-radiator, vibrations of more complex modes (for instance, offaxial mode) arise in it (for example, flexural vibrations). This leads to a disruption of the regime of the operation of the entire waveguide-radiator. Its natural resonance frequency changes and, as a consequence, additional experimental fitting of geometrical dimensions is required. Thus, a direct acoustic calculation of the waveguide-radiator as a waveguide of longitudinal waves becomes inaccurate. This manifests itself particularly clearly at high vibration amplitudes of the specified section of the waveguide-radiator. Second, the length of the specified exit section is small as compared with its diameter and, therefore, in this section the degree of strain (and, as a consequence, stress) along the section length is high, which substantially decreases the operational life span of such a waveguide-radiator at high amplitude.
3. Objects and Advantages
It is therefore a principal object and advantage of the present invention to provide a waveguide-radiator that is free from the drawbacks enumerated above, having an exit diameter close to the entrance diameter, and a gain factor much higher than unity, and having the following objectives:
1. To improve the quality of operation and to increase the operational life of a wave guide-radiator.
2. To increase the acoustic energy radiated into a load by a waveguide-radiator.
3. To increase the reliability of fastening various cutting and other tools on the waveguide radiator.
4. To increase the available radiation surface and the uniformity of the distribution of acoustic energy throughout the volume of an ultrasonic reactor.
5. To conduct ultrasonic treatment of the internal surfaces of thin extended channels and tubes.
6. To increase the intensity of acoustic radiation in the working medium of an ultrasonic reactor.
7. To increase the efficiency of conversion of electric energy of an ultrasonic generator into acoustic energy radiated into a load.